A variety of electronic devices such as cell phones, laptop computers, and personal digital assistants to name only a few, may be powered by one or more variable output DC power sources. A variable output DC power source may accept an unregulated input voltage and provide a variable output DC voltage and output current to a load of the electronic device. The unregulated input voltage may be an alternating current (AC) or DC input voltage.
Like other power supply sources, the variable output DC power source may be capable of providing a maximum output power to the load. At any time, the actual output power can be expressed as the product of the output voltage and output current. The instantaneous values of the output voltage/current of the variable output DC power source may be controlled by one or more control signals. These control signals may be provided according to a power management algorithm and may be the result of a set of sensing signal processing performed by power control circuitry. Other limitations may be imposed on the instantaneous output voltage/current of the variable output DC power source, but for clarity and simplicity, analysis herein is directed to the output power limiting features of the power control circuitry. Hence, if other limitations are not imposed, as the output voltage is reduced the output current can be increased as long as the product of the output voltage and output current is less than the maximum output power. Similarly, as the output current is reduced the output voltage can be increased as long as the product of the output current and output voltage is less than the maximum output power.
However, since power control circuits are relatively complicated and expensive, a conventional power control circuit limits the output current to a fixed maximum current level and limits the output voltage to a fixed maximum voltage level. The fixed maximum current and voltage levels are designed so that the product of each is at most equal to the maximum output power. Although a simple approach, this conventional power control circuit significantly reduces the safe operation region of the variable output DC power source.
Although the following Detailed Description will proceed with reference being made to illustrative embodiments, many alternatives, modifications, and variations thereof will be apparent to those skilled in the art. Accordingly, it is intended that the claimed subject matter be viewed broadly.